During your approved reservation slot, SSH into the console of the reserved domain with your portal username:
ssh <username>@console.<domain>.cosmos-lab.org
A console is a dedicated machine that gives access to all resources in its domain: from it you run the OMF commands (omf stat -t all is a good first look), hop to nodes as root, and keep files in your (shared, persistent) home directory.
Full connection reference — config recipes, ProxyJump, tunneling, troubleshooting: SSH Access. General access overview: Remote Access.